A product having a twisted shape, such as a male rotor or a female rotor in a screw compressor, is manufactured by a method in which a casting formed in a near net shape (a shape close to a final product shape due to a reduced machining margin) is produced by casting, and finished.
Patent Literature 1 discloses a core molding method for molding a core required for producing a casting formed in a near net shape by use of a core mold. In Patent Literature 1, the core mold is extracted in a horizontal direction from the core formed of a cured self-hardening sand while rotating the core mold disposed along a horizontal direction within a frame around its axis.